A soft start method applied to a switched capacitor converter circuit of a rechargeable battery

Abstract

A soft start method applied to a switched capacitor converter circuit of a rechargeable battery, characterized in that the method comprises the following steps: connecting an input end Vin of the switched capacitor converter circuit with a charger input source, and connecting an output end Vout of the switched capacitor converter circuit with an output source; charging a flying capacitor Cfly with a small current; after the flying capacitor Cfly is charged to a stable voltage across the flying capacitor Cfly, closing an additional current mirror, and in each clock cycle, first turning on MOS tubes Q2 and Q4 and turning off MOS tubes Q1 and Q3, and then turning on MOS tubes Q1 and Q3 and turning off MOS tubes Q2 and Q4, and simultaneously controlling the on time of Q1 and Q3 to be T / 2, and gradually increasing the on time of Q2 and Q4 from 100 nS to T / 2, so as to realize discharging of the flying capacitor Cfly and gradual increase of the charging current. The method is simple, does not need to change the circuit to realize suppression of the inrush current, and guarantees accuracy, stability and safety of the circuit.

Description

Technical Field

[0001] This invention relates to the field of integrated circuits, and more specifically, to a soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery. Background Technology

[0002] Currently, switched-capacitor voltage converters utilize controlled switches and capacitors to alter the ratio of output voltage to input voltage. In battery-powered applications, the circuit's multiplication factor automatically adjusts sequentially with voltage changes, ensuring a sufficiently high output voltage to drive subsequent circuits regardless of battery voltage variations. Therefore, as a high-efficiency, low-noise charge pump device, the switched-capacitor voltage converter (hereinafter referred to as a switched-capacitor converter) is widely used in various types of integrated circuits.

[0003] However, as a crucial component of the switched-capacitor converter, the initial capacitance value of the external flying capacitor Cfly can affect the converter's operating state. For example, before the converter's soft-start begins, if the voltage difference between the two plates of the flying capacitor is large, then when the soft-start begins and the state of the MOSFET in the converter changes, a momentary increase in charging current will occur. If this charging current surges and the peak amplitude is too high, it may damage the MOSFET and simultaneously momentarily pull down the input source voltage, causing abnormal circuit operation.

[0004] Therefore, there is an urgent need for a new soft-start method for switched-capacitor converters. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery. By controlling the cutoff state of the MOSFETs before soft-start, a suitable initial voltage difference is achieved between the two plates of the flying capacitor. Furthermore, the turn-on time of MOSFETs Q2 and Q4 is gradually extended during each soft-start cycle, thereby gradually releasing the initial charge of the flying capacitor.

[0006] The present invention adopts the following technical solution.

[0007] A soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery includes the following steps: Step 1, connecting the input terminal Vin of the switched-capacitor converter circuit to the input source of a charger, and connecting the output terminal Vout of the switched-capacitor converter circuit to the output source; Step 2, charging the flying capacitor Cfly; Step 3, after the flying capacitor Cfly is charged to a stable voltage across its terminals, in each clock cycle, first turning on MOSFETs Q2 and Q4 connected to the two terminals of the flying capacitor Cfly respectively, and turning off MOSFETs Q1 and Q3, then turning on MOSFETs Q1 and Q3 and turning off MOSFETs Q2 and Q4, so as to realize the discharge and charging current increase of the flying capacitor Cfly; wherein, the conduction time of MOSFETs Q2 and Q4 gradually increases to half a clock cycle in each clock cycle.

[0008] Preferably, in step 2, the process of performing current-limited charging on the flying capacitor Cfly is as follows: close the current mirror switch in the external current mirror unit, turn on MOSFET Q3, turn off MOSFETs Q1, Q2 and Q4, and use the external current mirror to charge the flying capacitor Cfly.

[0009] Preferably, the external current mirror is turned off after the flying capacitor Cfly is charged until the voltage across its two ends stabilizes.

[0010] Preferably, the external current mirror includes two PMOS transistors Q31 and Q32 connected in a mirror configuration; wherein the sources of both PMOS transistors are connected to the connection point between the input resistor Rin of the switched capacitor converter and the MOS transistor Q1; the drain and gate of the mirror PMOS transistor Q31 are grounded through the current mirror switch S1 and the reference current source, and the drain of the mirror PMOS transistor Q32 is connected to the connection point between the flying capacitor Cfly and the MOS transistor Q1.

[0011] Preferably, the width-to-length ratio of the mirrored PMOS transistors Q31 and Q32 is 1:1000; after the flying capacitor Cfly is fully charged, the initial conduction time of MOS transistors Q2 and Q4 is 100ns.

[0012] Preferably, in step 3, after the flying capacitor Cfly is charged until the voltage across its terminals stabilizes, the charge of the flying capacitor is Qfly = (Vin - Vout) * Cfly.

[0013] Preferably, in step 3, each clock cycle T refers to all clock cycles experienced by the circuit during the soft-start process.

[0014] Preferably, in each clock cycle, MOSFETs Q1 and Q3 are turned on and off for half a clock cycle each.

[0015] Preferably, the conduction time of MOSFETs Q2 and Q4 is t+(i-1)*t0, and the cutoff time of MOSFETs Q2 and Q4 is Tt-(i-1)*t0; where t is the shortest controllable conduction time of MOSFETs Q2 and Q4, t0 is the length of time that the conduction time of MOSFETs Q2 and Q4 in each cycle during the soft start process is extended compared to the previous cycle, i is the number of cycles after the soft start, and t+(i-1)*t0≤T / 2.

[0016] Preferably, at the end of the soft start, the charging current stabilizes at (V in -2V out ) / R in The output source voltage is stable at 2V. out Among them, V in V is the input source voltage before soft start. out R is the output source voltage before soft start. in The parasitic resistance of the charging cable at the circuit input terminal.

[0017] The beneficial effects of this invention are that, compared with the prior art, the soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery can achieve a suitable initial voltage difference between the two plates of the flying capacitor by controlling the off-state of the MOSFET before soft-start. Furthermore, it can gradually extend the on-time of MOSFETs Q2 and Q4 in each soft-start cycle, allowing the initial charge of the flying capacitor to be released gradually. This invention is simple, requires no changes to the circuit structure, and achieves surge current suppression simply by changing the MOSFET control method, ensuring the accuracy, stability, and safety of the circuit. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a switched capacitor converter circuit in the prior art of this invention;

[0019] Figure 2 This is a schematic diagram of the time curve of the control signal of a switched capacitor converter circuit in the prior art of this invention;

[0020] Figure 3 This is a schematic diagram of a switched capacitor converter circuit applied to a rechargeable battery according to the present invention;

[0021] Figure 4 This is a schematic diagram of the structure of an external current mirror unit in a switched capacitor converter circuit for rechargeable batteries according to the present invention.

[0022] Figure 5 This is a schematic diagram of the signal curve when a switched capacitor converter circuit for rechargeable batteries uses an external current mirror for charging a flying capacitor, according to the present invention.

[0023] Figure 6 This is a schematic diagram illustrating the soft-start working principle of a switched capacitor converter circuit applied to a rechargeable battery according to the present invention.

[0024] Figure 7 This is a schematic diagram of the time curve of the control signal in a soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to the present invention. Detailed Implementation

[0025] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0026] Figure 1 This is a schematic diagram of a switched-capacitor converter circuit in the prior art of this invention. (See diagram below.) Figure 1 As shown, commonly used switched-capacitor converters in the prior art include interconnected MOSFETs Q1, Q2, Q3, and Q4, which can be formed by connecting their source and drain in series. To achieve symmetrical arrangement, each MOSFET can also be configured as two symmetrical MOSFETs, for example, Q1 can be configured as including Q11 and Q21. Subsequently, the drain of Q1 in this branch can be connected to the circuit's input source Vin via the parasitic resistance Rin of the charging line. The connection point between Q2 and Q3 in this branch is connected to the circuit's output source Vout, and the source of Q4 is grounded. To achieve the output voltage generation method of the charge pump in this circuit, the upper and lower plates of a flying capacitor Cfly are connected to the connection points of Q1 and Q2, and Q3 and Q4, respectively.

[0027] In traditional switched-capacitor converters, Q2 and Q4, or an additional NMOS current mirror, are typically turned on first, allowing the output source Vout to charge the flying capacitor Cfly through Q2 and Q4 or the additional NMOS current mirror Q4. Once stable, the voltage difference across Cfly will be Vout. Subsequently, the soft-start process begins.

[0028] Figure 2 This is a schematic diagram of the time curve of the control signal in a switched-capacitor converter circuit according to the prior art of this invention. Figure 2 As shown, after soft start is enabled, Q1 and Q3 are turned on first, while Q2 and Q4 are turned off. This process lasts for half a cycle, after which Q1 and Q3 are turned off and Q2 and Q4 are turned on. After several cycles of the above process, the soft start is completed.

[0029] from Figure 2As can be seen from the diagram, since Cfly has an initial charge and its initial voltage difference is Vout, when soft-start begins, based on the initial charge on Cfly and the conduction states of Q1 and Q3, Cfly will execute the charging process quickly and sufficiently, causing a surge in the charging current Iin. Figure 2 As can be seen, the peak current of the charging current surge exceeds the stable value after the soft-start of the charging current. Since current surges may cause a rapid drop in the input source voltage, leading to circuit abnormalities, and may also damage the MOSFETs in the circuit, this invention provides an improved switched-capacitor converter.

[0030] Figure 3 This is a schematic diagram of a switched-capacitor converter circuit applied to a rechargeable battery according to the present invention. Figure 3 As shown, a soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery includes the following steps: Step 1, connecting the input terminal Vin of the switched-capacitor converter circuit to the input source of the charger, and connecting the output terminal Vout of the switched-capacitor converter circuit to the output source; Step 2, performing current-limited charging on the flying capacitor Cfly; Step 3, after the flying capacitor Cfly is charged to a stable voltage across its terminals, in each clock cycle, first turning on MOSFETs Q2 and Q4 connected to the two terminals of the flying capacitor Cfly respectively, and turning off MOSFETs Q1 and Q3, then turning on MOSFETs Q1 and Q3 and turning off MOSFETs Q2 and Q4, so as to realize the discharge and charging current increase of the flying capacitor Cfly; wherein, in each clock cycle, the conduction time of MOSFETs Q2 and Q4 gradually increases to half a clock cycle.

[0031] It is understandable that in step 2 of this invention, in order to prevent excessive charge released instantaneously by the flying capacitor Cfly during the initial soft-start process from affecting the soft-start circuit, the traditional technical solution of turning on Q2 and Q4 before soft-start is changed. Specifically, this invention achieves this by gradually increasing the conduction time of MOSFETs Q2 and Q4.

[0032] Figure 4 This is a schematic diagram of the external current mirror unit in one embodiment of a switched capacitor converter circuit applied to a rechargeable battery according to the present invention. Figure 4 As shown, preferably, in step 2, the process of performing current-limited charging on the flying capacitor Cfly is as follows: close the current mirror switch in the external current mirror unit, turn on MOSFET Q3, and turn off MOSFETs Q1, Q2 and Q4, using the external current mirror to charge the flying capacitor Cfly; or, without using the external current mirror unit, turn on MOSFETs Q1 and Q3, turn off MOSFETs Q2 and Q4, and use the MOSFETs in the switched capacitor converter to charge the flying capacitor Cfly.

[0033] This invention allows for two different methods to pre-charge the flying capacitor. For a simpler circuit structure without adding extra circuitry, only MOSFETs Q1 and Q3 can be turned on, while the other two are turned off. However, charging MOSFETs Q1 and Q3 may cause an initial surge; that is, when the charger's input voltage increases instantaneously, the input current may rise instantaneously, potentially damaging related components in the circuit.

[0034] In this improved version of the invention, before soft-start, a small current-limited charging method is used to charge the flying capacitor by turning on an external PMOS current-limiting mirror circuit and MOSFET Q3. After charging, the voltage difference between the two plates is no longer equal to Vout, but equal to Vin-Vout. Since the initial value of the voltage on Cfly is usually not significantly different from the voltage difference between the charger's input source and the output battery, this method, to a certain extent, suppresses the generation of initial surges.

[0035] Preferably, if an external current mirror is used for charging, the external current mirror is turned off after the flying capacitor Cfly has been charged to a stable voltage across its terminals.

[0036] In this invention, if an external current mirror is used to assist in the implementation of the function, the external current mirror unit only remains in working state during step 2, when the flying capacitor is charging. When the circuit enters the process of cyclically turning on and off MOS transistors Q1 to Q4, there is no need to use the corresponding current mirror circuit. At this time, the switch in the current mirror circuit is turned off.

[0037] Preferably, the external current mirror includes two PMOS transistors Q31 and Q32 connected in a mirror configuration; wherein the sources of both PMOS transistors are connected to the connection point between the input resistor Rin of the switched capacitor converter and the MOS transistor Q1; the drain and gate of the mirror PMOS transistor Q31 are grounded through the current mirror switch S1 and the reference current source; the drain of the mirror PMOS transistor Q32 is connected to the connection point between the flying capacitor Cfly and the MOS transistor Q1.

[0038] In this invention, the external current mirror unit includes two PMOS transistors, a switch, and a reference current source. When the switch is closed, the reference current source provides a reference current to the first transistor Q31. Since Q31 and Q32 are mirror images of each other, and the current from the reference current source is relatively small, the charging current can be limited. In this invention, the current value of the reference current source is 100μA, which, multiplied by the current mirror's magnification factor of 1000, yields a charging current of 100mA.

[0039] Figure 5This is a schematic diagram of the signal curve when a switched capacitor converter circuit for rechargeable batteries uses an external current mirror for charging a flying capacitor, according to the present invention. Figure 5 As shown, after charging with a current-limiting current, the charge of the flying capacitor steadily increases over time. At the same time, since the source and drain currents of the MOSFETs in the switched capacitor converter are small and controlled by the current mirror, there will be no sudden changes.

[0040] Preferably, the magnification of the current mirror is 1:1000; after the flying capacitor Cfly is fully charged, the initial conduction time of MOSFETs Q2 and Q4 is 100ns.

[0041] In this invention, the magnification of the current mirror can be preset according to the aspect ratio of the two MOSFETs in the current mirror. Furthermore, when the initial conduction time of MOSFETs Q2 and Q4 is short, current oscillation and overshoot can be effectively prevented after the switched-capacitor converter has started operating.

[0042] Preferably, in step 3, after the flying capacitor Cfly is charged to a stable voltage across its terminals, the charge of the flying capacitor is Qfly = (Vin - Vout) * Cfly.

[0043] It is understandable that, as mentioned above, after the flying capacitor Cfly is charged to a stable voltage across its terminals, the charge of the flying capacitor will become the product of the voltage difference across its terminals and the capacitance.

[0044] In addition, in step 3 of this invention, the traditional soft-start process with unchanged MOS transistor turn-on and turn-off times has been modified, and the turn-on and turn-off times of MOS transistors Q2 and Q4 have been modified.

[0045] Figure 6 This is a schematic diagram illustrating the soft-start working principle of a switched-capacitor converter circuit applied to rechargeable batteries according to the present invention. Figure 6 As shown, it can be understood that although the turn-on and turn-off times of Q2 and Q4 have been changed in this invention, the turn-on and turn-off times of Q1 and Q3 have not been changed. This allows the charging current sufficient time to recover to a stable current after each small surge.

[0046] Specifically, during the first clock cycle of the soft-start, the on-time of MOSFETs Q2 and Q4 is the shortest controllable on-time t, and the off-time of MOSFETs Q2 and Q4 is Tt. In one embodiment of the present invention, the value of t can be 100ns. Generally, in order to minimize the time of the current rise during the first soft-start cycle, i.e., the current rise with the largest surge current slope, the value of t can be set to the shortest controllable on-time of the MOSFETs by the circuit.

[0047] Figure 7 This is a schematic diagram of the time curve of the control signal in a soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to the present invention. Figure 7 As shown, in this invention, during each time period after the soft start begins, the duty cycle of the control signals for the gates of Q2 and Q4 gradually increases to 1 / 2.

[0048] Preferably, in step 3, each clock cycle T refers to all clock cycles experienced by the circuit during the soft-start process.

[0049] According to the present invention, after the soft-start process has gone through about a few clock cycles, the value of its output charging current gradually stabilizes, and at this time the charge of the flying capacitor is also gradually released into the circuit.

[0050] Preferably, in each clock cycle, MOSFETs Q1 and Q3 are turned on and off for half a clock cycle each.

[0051] Preferably, the conduction time of MOSFETs Q2 and Q4 is t+(i-1)*t0, and the cutoff time of MOSFETs Q2 and Q4 is Tt-(i-1)*t0; where t0 is the length of time that the conduction time of MOSFETs Q2 and Q4 in each cycle during the soft start process is longer than that of the previous cycle, i is the number of cycles after the soft start, and t+(i-1)*t0≤T / 2.

[0052] After controlling the conduction time of Q2 and Q4 in the first cycle, the conduction time of Q2 and Q4 gradually increases in each subsequent cycle of the soft-start process. In this invention, the length of the increase in conduction time in each cycle can be reasonably designed so that in the cycle ending the soft-start, the conduction time of Q2 and Q4 is slightly less than or exactly equal to half a cycle.

[0053] Preferably, at the end of the soft start, the charging current stabilizes at (V in -2V out ) / R in The output source voltage is stable at 2V. out Among them, V in V is the input source voltage before soft start. out R is the output source voltage before soft start. in The parasitic resistance of the charging cable at the circuit input terminal.

[0054] It is understood that when the soft start ends in this invention, the charging current will stabilize at (V). in -2V out ) / R inThis is because, with the action of the flying capacitor Cfly, the drain voltage of Q1 is reduced to twice the value of Vout through the discharge of Cfly in each cycle. Thus, the charging current is equal to the ratio of the difference between the input source and output source voltages to the parasitic resistance Rin of the charging line.

[0055] from Figure 7 It can be clearly seen that, through the method of this invention, in the initial stage of soft start, the surge current is discharged rapidly in a very short time each time, thus avoiding excessively high surges. In the later stage of soft start, the slope of the surge current decreases, while the release time of the surge current in each cycle is gradually extended. Even so, the increase in charging current Iin caused by the surge current is not too high, thus making the soft start process relatively smooth and slowly increasing the charging current Iin to a stable state, and finally successfully completing the soft start process.

[0056] The beneficial effects of this invention are that, compared with the prior art, the soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery can achieve a suitable initial voltage difference between the two plates of the flying capacitor by turning on the external current-limiting mirror and controlling the off state of the MOSFET before soft-start. Furthermore, it can gradually extend the on-time of MOSFETs Q2 and Q4 in each soft-start cycle, allowing the initial charge of the flying capacitor to be released gradually. This invention is simple, requires no changes to the circuit structure, and achieves surge current suppression simply by changing the MOSFET control method, ensuring the accuracy, stability, and safety of the circuit.

[0057] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery, characterized in that, The switched-capacitor converter circuit includes MOSFETs Q1, Q2, Q3, and Q4, and a flying capacitor Cfly; the source of MOSFET Q1 is connected to the drain of MOSFET Q2, the source of MOSFET Q2 is connected to the drain of MOSFET Q3, and the source of MOSFET Q3 is connected to the drain of MOSFET Q4; the drain of MOSFET Q1 is connected through the parasitic resistance of the charging cable. Connect the input terminal of the circuit The connection point between MOSFETs Q2 and Q3 is connected to the output terminal of the circuit. The source of MOSFET Q4 is grounded; The two ends are respectively connected to the connection points of MOSFET Q1 and MOSFET Q2, and the connection points of MOSFET Q3 and MOSFET Q4; the method includes the following steps: Step 1: Connect the input terminal Vin of the switched capacitor converter circuit to the charger input source, and connect the output terminal Vout of the switched capacitor converter circuit to the output source. Step 2: Perform current-limited charging on the flying capacitor Cfly; Step 3: After the flying capacitor Cfly is charged to the point where the voltage at both ends is stable, in each clock cycle, first turn on the MOS transistors Q2 and Q4 connected to the two ends of the flying capacitor Cfly respectively and turn off the MOS transistors Q1 and Q3, then turn on the MOS transistors Q1 and Q3 and turn off the MOS transistors Q2 and Q4, so as to realize the discharge of the flying capacitor Cfly and the increase of the charging current. In each clock cycle, the conduction time of MOSFETs Q2 and Q4 gradually increases to half a clock cycle.

2. The soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 1, characterized in that: In step 2, the process of performing current-limited charging on the flying capacitor Cfly is as follows: Close the current mirror switch in the external current mirror unit to turn on MOSFET Q3 and turn off MOSFETs Q1, Q2 and Q4, and use the external current mirror to charge the flying capacitor Cfly.

3. The soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 2, characterized in that: After the flying capacitor Cfly is charged to a stable voltage across its terminals, the external current mirror is turned off.

4. The soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 3, characterized in that: The external current mirror includes two PMOS transistors Q31 and Q32 connected in a mirror-like manner; In this configuration, the sources of the two mirror-connected PMOS transistors are both connected to the connection point between the input resistor Rin of the switched capacitor converter and the MOS transistor Q1. The drain and gate of the mirrored PMOS transistor Q31 are grounded through the current mirror switch S1 and the reference current source. The drain of the mirrored PMOS transistor Q32 is connected to the connection point of the flying capacitor Cfly and the MOS transistor Q1.

5. The soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 4, characterized in that: The width-to-length ratio of the mirrored PMOS transistors Q31 and Q32 is 1:1000; After the flying capacitor Cfly is fully charged, the initial conduction time of the MOSFETs Q2 and Q4 is 100ns.

6. The soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 5, characterized in that: In step 3, after the flying capacitor Cfly is charged until the voltage across its terminals stabilizes, the charge of the flying capacitor is Qfly = (Vin - Vout). Cfly.

7. A soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 6, characterized in that: Each clock cycle in step 3 This refers to all clock cycles experienced by the circuit during the soft-start process.

8. The soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 7, characterized in that: Within each clock cycle, MOSFETs Q1 and Q3 are turned on and off for half a clock cycle each.

9. A soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 8, characterized in that: The conduction times of the MOSFETs Q2 and Q4 are: The cutoff times of the MOS transistors Q2 and Q4 are... ; in, This refers to the shortest controllable on-time of the MOSFETs Q2 and Q4. This refers to the length of time during which the on-time of MOSFETs Q2 and Q4 extends compared to the previous cycle during the soft-start process. This represents the number of cycles after a soft start, and has... .

10. A soft-start method for a switched-capacitor converter circuit applied to a rechargeable battery according to claim 9, characterized in that: When the soft start ends, the charging current stabilizes at The output source voltage is stabilized at ; in, This is the input source voltage before soft start. This is the output source voltage before soft start. The parasitic resistance of the charging cable at the input terminal of the circuit.

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